| Summary: | Pitch pine (<i>Pinus rigida</i> Mill.) is native to North America and has a strong resistance to pine wood nematodes (PWNs). The PWN resistance mechanism of this tree species has yet to be discovered. In this work, we found that the spreading of inoculated PWNs in the branch of <i>P. rigida</i> was significantly suppressed compared to those in the branches of <i>Pinus densiflora</i> (Sieb. et Zucc.) and <i>Pinus koraiensis</i> (Sieb. et Zucc.). Dipping of PWNs in the resins isolated from <i>P. rigida</i> significantly suppressed the PWN mobility and conferred significantly higher PWN mortality compared to those in the resins from <i>P. densiflora</i> and <i>P. koraiensis</i>. All PWNs dipped in <i>P. rigida</i> resin were killed after six days, but more than 50% of the PWNs dipped in the resin from <i>P. densiflora</i>, and <i>P. koraiensis</i> were still alive after six days. The phytochemical analysis of resins revealed that <i>P. rigida</i> resin contained little or no amount of sesquiterpenes compared to those from <i>P. densiflora</i> and <i>P. koraiensis</i>. However, <i>P. rigida</i> resin contained rich amounts of diterpenes, among which dehydroabietic aldehyde, methyl dehydroabietate, and methyl abietate were uniquely detected. Particularly, two pinosylvin stilbenes (<i>trans</i> and <i>cis</i>-3,5-dimethoxystilbene) were accumulated in <i>P. rigida</i> resin, which were not detected in the resins from <i>P. densiflora</i> and <i>P. koraiensis. cis</i>-3,5-Dimethoxystilbene showed high nematicidal activity but not in <i>trans</i>-3,5-dimethoxystilbene. Conclusively, PWN resistance of <i>P. rigida</i> may be due to the toxic chemicals in the resin, in which <i>cis</i>-3,5-dimethoxystilbene may contribute to PWN toxicity. This work is the first demonstration that resin from PWN-resistant <i>P. rigida</i> directly affected PWN mobility and mortality, probably due to toxic phytochemicals in the resin.
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